[root@server0 maketest2]# cat foo.c addnum.c

#include<stdio.h>

extern int addnumbers(int a,int b);

int main()

{

   int sum;

   int x=5;

   int y=8;

   sum=addnumbers(x,y);

   printf("sum of %d and %d is %d\n",x,y,sum);

   return 0;

}

#include<stdio.h>

int addnumbers(int a,int b)

{

   int sum;

   sum=a+b;

   return sum;

}

[root@server0 maketest2]# gcc -o foo foo.c addnum.c

[root@server0 maketest2]# ll

-rw-r--r--. 1 root root   83 Apr 12 03:06 addnum.c

-rwxr-xr-x. 1 root root 8579 Apr 12 03:14 foo

-rw-r--r--. 1 root root  177 Apr 12 03:13 foo.c

[root@server0 maketest2]# ./foo

sum of 5 and 8 is 13

[root@server0 maketest2]# cat Makefile

hello: foo.o addnum.o

   gcc -o hello foo.o addnum.o

foo.o: foo.c

   gcc -c foo.c

addnum.o: addnum.c

   gcc -c addnum.c

clean:

   rm -f *.o hello

[root@server0 maketest2]# make

gcc -c foo.c

gcc -c addnum.c

gcc -o hello foo.o addnum.o

[root@server0 maketest2]# ./hello

sum of 5 and 8 is 13